Open center control of variable pumps

ABSTRACT

Control of the displacement of a variable displacement pump is achieved by the use of a standard opencenter type of control valve and pump displacement controls that include a sensor valve. The control functions that are achieved include system standby at low pressure and minimum displacement thereby minimizing power loss and heat rise.

United States Patent [191 Johnson et a1.

[ OPEN CENTER CONTROL OF VARIABLE PUMPS [75] Inventors: Raymond E. Johnson, Muncie;

Wendell E. Miller, Warsaw, both of 1nd.; Kenneth G. McMillen,

deceased, late of New Castle, lnd.; Leanne S. McMillen, administratrix, Fort Wayne, Ind.

[73] Assignee: Borg-Warner Corporation, Chicago,

Ill.

[22] Filed: July 13, 1972 [21] Appl. No.: 271,303

[52] US. Cl. 60/452, 417/212 [51] Int. Cl. Fl6h 39/46 [58] Field of Search 60/452, 445; 417/212 [56] References Cited UNITED STATES PATENTS 2,238,060 4/1941 Kendrick 60/452 [451 Jan. 29, 1974 3,250,227 5/1966 Kouns 91/473 3,366,064 1/1968 Stephens et a1 60/452 X 3,406,850 10/1968 l-lancox 60/452 X 3,444,689 5/1969 Budzich 60/445 X Primary Examiner-Edgar W. Geoghegan Attorney, Agent, or Firm-Donald W. Banner et a1.

[ ABSTRACT Control of the displacement of a variable displacement pump is achieved by the use of a standard opencenter tyg 9Q control \galve and pump dis; placement controls that include a sensor valve. The control functions that are achieved include system standby at low pressure and minimum displacement thereby minimizing power loss and heat rise.

20 Claims, 6 Drawing Figures OPEN CENTER CONTROL OF VARIABLE PUMPS THE INVENTION Hydraulic systems utilizing fixed displacement pumps and open center control valves are used extensively and have been for many years. Multiple spool control valves of this type include a neutral flow passage that connects the valve inlet port with the valve outlet port when all valve spools are in a neutral position. This provides a fluid path to convey all pump discharge from the valve inlet port to the valve outlet port and to the fluid sump or reservoir when no power is needed, thereby holding the fluid pressure, power at the pump increases as functions of both the number of valve spools and the flow rate, so that excessive neutral flow pressures, power losses, and heat rises are often encountered in system design.

Another disadvantage of the standard type of open center system utilizing a fixed displacement pump is that, when utilizing only a part of the pump displacement, the unused pump flow results in a power loss as a function of the percentage of flow that is bypassed and of the instantaneous working pressure of the system. Thus, it is not unusual to be wasting as much power as is being used at a given time.

Variable displacement pumps with pressure compensator controls have been used in an attempt to achieve better system efficiency. The disadvantages of this type of system are that: the standby pressure is the maximum system pressure; and operation of a fluid motor at low pressure and low flow involves the throttling of a large pressure drop across the valves which constitutes a large power loss.

Load-responsive systems are one solution to the inadequacies of both the open center and pressure compensated systems. An example of an advanced system of this type is disclosed in U.S. Pat. No. 3,526,247. A load responsive system has many advantages, but it includes the disadvantage of requiring a control valve of special design and increased complexity.

The system of the present invention overcomes the disadvantages of the open center system by providing low standby pressure at the minimum displacement of a piston pump, as well as at low pressure. Also, the excessive power loss during partial flow use of the open center system is eliminated because the system of the present invention produces only the flow that is required, that is, as long as only one valve spool is actuated at any one time.

The system of the present invention also overcomes the disadvantages of the pressure compensated system. The present invention achieves not only standby pressure at minimum pump displacement as does the pressure compensated system, but also it achieves standby pressure conditions at low system pressure. Also, the high power loss caused by throttling flow to a motor operating at low pressure and low flow, as experienced by pressure compensated systems, is eliminated by the present invention. In the present invention, only the necessary flow and pressure are pumped, as long as only one valve spool is actuated at any one time.

The system of the present invention also overcomes the disadvantage of the load responsive system, or an even less complex and less costly closed center valve can be designed especially for the system disclosed herein.

Included in the disclosed variations of the present invention are two designs that achieve greater precision of control of the pump displacement by the use ofa mechanical feedback between the displacement control mechanism of the pump and the sensor valve that controls the displacement control mechanism. One of these variations utilizes a spring as a portion of the feedback mechanism, and the other includes a piston in the displacement control mechanism as a portion of a coaxial piston feedback mechanism. Both of these variations are adaptable for use with a standard open center valve having series connected neutral flow passages.

THE DRAWINGS FIG. 1 is a schematic of the system that includes a cross sectional view of the sensor valve and a cross sectional view of an open center control valve.

FIG. 1A is a modification of the system shown in FIG. 1.

FIG. 2 is a schematic of the system that includes a cross sectional view of a closed center control valve having parallel connected control signal valves.

FIG. 3 is a schematic of the system in which the sensor valve includes a third or bypass position.

FIG. 4 is a cross section of a sensor valve that includes third and fourth bypass positions.

FIG. 5 is a schematic of the system that includes a cross section of a sensor valve having coaxial piston feedback.

Referring to FIG. 1, a variable displacement pump of the axial piston type includes a rotating cylinder barrel 11 containing a plurality of pistons 12 and rotated by a drive shaft 13. The pump 10 also includes a fluid actuated displacement control mechanism 14 which is comprised of a variable inclination swash plate 15 mounted on trunnion bearings, not shown, and adapted to impart reciprocating movement to the pistons 12, a control piston 16 adapted to impart a displacement decreasing movement to the swash plate 15, and a spring 17 adapted to urge the swash plate 15 toward a higher displacement inclination.

The system of FlG. 1 also includes a sensor valve 20 which includes a body 21 having a plunger bore 22 and ports 23, 24, 25, 26 and which also includes valve plunger 27 and and a bias force means or bias spring 28.

An open center control valve 30 is also included in FIG. 1. The control valve 30 includes a valve body 31 having an inlet port 32, an outlet port 33, work ports 34a and 34b, work ports 35a and 35b, and valve spool bores 36a and 366. Valve spools 37a and 37b are slidably fitted in the bores 36a and 36b and resiliently held in their neutral positions as shown by means of centering springs, not shown, which are included in cap 38.

The control valve 30 of FIG. 1 includes return passages 40a, 40b, 40c and pressure passages 41a, 41b,

Thus the control valve 30 is a standard type of open center control valve with the exception of the restrictor means or orifice 45 and the control signal port 46.

The hydraulic system of FIG. 1 also includes a reservoir or fluid sump symbolized by the separate sumps 50a, 50b and 500 and includes a pilot relief valve 51 having a seat 52, a poppet 53, and a spring 54.

Referring again to the sensor valve 20, the bias spring 28 is adapted to urge plunger 27 to the right by means of a spring adapter 29. The left end of spring 28 is held by a spring adapter 56 and a push rod 57 which is interposed between the spring adapter 56 and the swash plate 15. However, the operation of the system .will first be described without the pushrod 57 and with the adapter 56 rigidly fixed to the body 21 of the sensor valve 20 by a mechanical connection, as shown in FIG.

Operation of the FIG. 1A system is as follows: the pump receives fluid from the sump 50a by a conduit 60. Pressurized fluid is discharged from the pump 10 via conduits 61, 62 and 63 to the inlet port 32 of the control valve 30 and through the control valve 30 to the sump 500 via the pressure passage 41a, the neutral flow passage 42 which is comprised of the control signal valves 43a and 43b and the passage 44, the restrictor meanS 45, the return passage 40b, the outlet port 33, and a conduit 64.

This flow of fluid from the pump 10 to the sump 500 via the restrictor 45 results in a pressure drop across the restrictor 45 which causes an increase in fluid pressure between the pump 10 and the restrictor 45. This increase of pressure is applied to a fluid responsive area comprised of projected areas 65a and 65b of plunger 27 of the sensor valve via the control signal port 46, control signal conduits 70 and 71, and the port 26, so that the projected areas 650 and 65b cooperate with a portion of body 21 and the space therebetween to form a fluid actuator means 59 and to move the plunger 27 from the neutral position as shown, to the left against the bias force of the spring 28. This movement of the plunger 27 to the left to a second operating position is effective to connect pump pressure from the pump 10 to a control piston 16 via the conduits 61 and 66, the port 25, a reduced plunger portion 67, the port 23, and a conduit 68. Thus the increase in pump pressure as caused by fluid flow across the orifice 45 is used as a control signal pressure and it is effective to move the plunger 27 to the left, to direct pump flow to the piston 16, to decrease the inclination of the swash plate 15, and to decrease the displacement of the pump 10 whenever the force developed by the fluid actuator means 59 is sufficient to overcome the bias force of the spring 28.

This reduction in displacement as caused by neutral flow of fluid through the control valve 30 occurs in the standby condition of the apparatus. That is, the valve spools 37a and 37b are in their neutral positions, as shown, and they are blocking the work ports 34a, 34b, 35a and 35b from both the pressure passages 41 and the return passages so that fluid actuated devices or fluid motors attached to the work ports 34 and 35 are not being'actuated. In this standby condition, the displacement of the pump 10 is low, that is, the output of the pump 10 is only what is required to cause a pressure rise across the-restrictor 45 that will cause a force large enough to overcome the spring 28.

When either valve spool 37a or 37b is actuated in either direction, the respective control signal valve 4311 or 43b is closed or restricted. The-closing or restricting of a control signal valve is effective to reduce the fluid pressure that is applied to the fluid actuator means 59 because of the reduction or the elimination of flow from the pump 10 and across a control signal valve 43 and thus the reduction or elimination of flow across the orifice 45. A reduction in fluid pressure in the fluid actuator means 59 allows the spring 28 to move the plunger 27 to the right to a first operating position and to force fluid from the fluid actuator means 59 to the sump 50c via the port 26, the conduits 71 and 70, the control signal port 46, the restrictor 45, the passage 40b, the outlet port 33 and the conduit 64.

This movement of the plunger 27 to the right establishes a flow path across the sensor valve 20 and allows the spring 17 to increase the displacement of the pump 10 by increasing the inclination of the swash plate 15, by moving the piston 16 to the right, and by discharging fluid from the piston 16 to the sump 50b via the conduit 68, the port 23, a reduced portion 72 of the plunger 27, the port 24, and a conduit 73.

Thus it can be seen that actuation of either of the valve spools 37a or 37b is effective not only to connect a work port 34 or 35 to a pressure passage 41 but also to increase the displacement of the pump 10.

A buildup in fluid pressure beyond that required by a fluid motor attached to a work port 34 or 35 is prevented by designing the valve spools 37a and 37b so that less movement of the valve spools 37a and 37b is required to connect a work port 34 or 35 to a pressure passage 41 or tea return passage 40 that is required to restrict or to block a control signal valve, 43a or 43b, sufficiently to cause an increase in the displacement of the pump 10.

The relief valve 51 is connected to the pump 10 by conduits 61, 62 and 74 and to the fluid actuator means 59 by conduits 75 and 71 and the port 26. Pump pressure above a predetermined value is effective to move the poppet 53 away from the seat 52 in opposition to the spring 54, sending fluid to actuator 59, moving the plunger 27 to the left establishing a flow path across the sensor valve 20, directing pump outlet fluid to the control piston 16, and decreasing the displacement of the pump 10.

Referring to FIG. 1, operation of the system with the push rod 57 included is the same as previously described, except that, inclusion of the push rod 57 provides mechanical feedback to the sensor valve 20.

The movement of the swash plate 15 is used to change the bias force of the spring 28 through the connection formed by the push rod 57 and the adapter 56, so that a change in displacement of the pump 10, as called for by change in control signal pressure applied to the actuator 59 and the movement of the plunger 27, results in a change in bias force which opposes this movement of the valve plunger 27 that has been caused by the change in control signal pressure. This results in a proportional relationship between control signal pressure and pump displacement. Operation of the FIG. 1 configuration includes movement of spool or valving element 37a or 37b from the neutral position as shown in FIG. 1 and is effective to reduce the conductance or flow path opening of control signal valve 43a or 43b proportional to the movement of valving element 37a or 37b, thereby restricting fluid flow and reducing the fluid flow rate from the pump and the conduit 61 to the sump 500 via the restrictor means 45 in proportion to the movement of spool 37a or 37b and in proportion v to the reduction in conductance of a control signal valve 43a or 43b.

This reduction of fluid flow rate across the restrictor 45 results in a decrease in the pressure drop across the restrictor 45 which is proportional to this change in flow rate and which is also proportional to the movement of valve spool 37a or 37b, so that the fluid pressure or control signal pressure at the control signal port 46 decreases proportional to the movement of a valve spool 37a or 37b.

The valve plunger 27 or the sensor valve is designed to move a distance that is proportional to the control signal pressure applied to the responsive areas 65a and 65b so that the movement of the valve plunger 27 is proportional to both the control signal pressure and to the movement of valve spool 37a or 37b which controls the control signal pressure.

This proportional response of the valve plunger 27 to control signal pressure is the result of the fluid responsive areas 650 and 65b developing a force proportional to the control signal pressure and to the bias means or spring 28 which produces a force to resist the movement of the valve plunger 27 that is proportional to movement of the valve plunger 27.

Thus there is a first level or magnitude of control sig nal pressure that will move the valve plunger away from a first position in which the surface of the area 65b is butted against the right end of the housing 21 and there is a second and higher level of control signal pressure that is required to move the valve plunger 27 to the neutral position as shown in FIG. 1 and also there is a third level of control signal pressure that is required to move the valve plunger to the left of the neutral position and to the second operating position wherein the port 23 is communicated with the port 25 via the reduced plunger portion 67.

A feedback means is included in FIG. 1 that is effective to change the level or magnitude of control signal pressure that is required to move the valve plunger 27 to the neutral position and to the other positions. This feedback means consists of the push rod 57 and its translating ofa change in displacement of the pump 10 is the result of movement of the displacement control mechanism 14 which is movable from minimum to maximum displacement limits and which results in a change in the inclination of the swash plate 15.

A change in displacement is proportional to a change in the inclination of the swash plate 15 and a change in the inclination of swash plate 15 moves the push rod 57 and the spring adapter 56 proportional to this change in displacement so that the load of the spring 28 and the control signal pressure required to move the valve plunger 27 to a given position are both changed proportional to a change in the displacement of the pump 10.

Thus a movement of valve spool 37a or 37b results in a control signal pressure and in a movement of the valve plunger 27 that are both proportional to the movement of valve spool 370 or 37b, and the movementof the valve plunger 27 to a position on either side of neutral results in fluid flow into or out of the control piston 16 and a resultant change in the displacement of the pump 10. This change in displacement continues until the push rod 57 is moved by the swash plate 15 sufficiently to change the control signal pressure that is required to move the valve plunger 27 to the neutral position to be equal to the control signal pressure being produced by the movement of valve spool 37a or 37!).

That is, the valve plunger 27 moves to the neutral position as shown and locks the displacement of the pump 10 and the inclination of the swash plate 15 to control the displacement of the pump 10 proportionalto movement of valve spool 370 or 37b and the magnitude of the control signal pressure.

Referring now to the FIG. 2 embodiment, a variable displacement pump 10 has a displacement control mechanism which includes: a swash plate 15, a control piston 16 that is adapted to increase the displacement of the pump 10, a spring 17 that is adapted to decrease the displacement of the pump 10 and a minimum displacement stop 81.

The system of FIG. 2 includes a sensor valve 83 that is symbolically represented and that includes first and second operating positions which are represented by boxes 84 and 85. The sensor valve 83 is operated to the first operating position 84 by a bias force or spring 28 and to the second operating position 85 by a fluid actuator 59.

The FIG. 2 configuration also includes a closed center control valve 88 which includes a body 89 and valve spools 90a and 90b. The operation of control valve 88 is the same as that of control valve 30, except that, the body 89 and the spools or movable valving members 90a and 90b have been modified to provide control signal value lands or valves 91a, 91b, 92a and 92b which are parallel-connected and which are normally closed, whereas the control signal valves 43a and 43b of the FIG. 1 configuration were connected in series and were normally open.

The control signal valves 91a and 91b, 92a and 92b are comprised of the notches 93a, 93b, 94a and 94b and of the valve spool bores 36a and 36b where they intersect the pressure passages 41b and 41c. Thus each of the control signal valves 91a, 91b, 92a and 92b includes a first port which is a portion of a passage 41 and all of these first ports are interconnected by the passage 41 and each of the control valves 91a, 91b, 92a and 92b includes a second port comprised by a control signal pressure chamber 103.

In standby operation the valve spools 90a and 9012 are held in their neutral positions as shown, and all of the control signal valves 91 and 92 are closed, so that the fluid pressure in the control port 46 is approximately the same as the fluid pressure in the sump 50c, and the fluid pressure in conduit 97 and actuator 59 is also equal to sump pressure.

The spring 28 is capable of moving the sensor valve 83 to the first operating position 84 because of the low pressure in the actuator 59, and a fluid path 98 connects the control piston 16 to the sump 50b via conduits 68 and 73, thereby allowing the spring 17 to move the swash plate 15 to the minimum displacement position as limited by the stop 81.

The displacement of the pump 10 at standby conditions is limited by the minimum displacement stop 81, and the pump pressure-at standby conditions is limited by a standby path 99 in the first position 84 of the'sensor valve 83 and a standby relief valve 101 which coopcrate to discharge the standby pump flow from the pump 10 to the sump 50b via conduits 61, 66, and 102.

In actual design practice, as will be apparent to those familiar with the art, the fluid path 98 would be established before the standby path 99 is established as the sensor valve 83 is actuated from the second operating position 85 to the first operating position in which the displacement of the pump 10 would be reduced by flow from the piston 16 to the sump 50c without loss of fluid from pump 10 through the standby path 99 and the standby relief valve 101.

The movement of either of the valve spools 90a or 90b, in either direction from the neutral position to an operating position, is effective to open a fluid path from a notch 93 or 94 to a pressure passage 41b or 41c, thereby pressuring the control signal pressure chamber 103, the port 46, the conduit 97, and the actuator 59 to move the sensor valve 83 to the second operating position 85 and thus to increase the displacement of the pump 10 by flow of pump fluid from the conduit 66 to the conduit 68 and the piston 16 via a flow path 104.

Another type of sensor valve is shown in FIG. 3. The system of FIG. 3 includes a pump 10 and a displacement control mechanism 14 that are similar to the FIG. 1 configuration, a symbolical representation of a bypass type sensor valve 110 that includes a third operating position 113, and a symbolical representation of a control valve 115 that includes working sections 116 and 117.

The working sections 116 and 117 are provided with pump flow via load checks 118 and 1 19 which are common to the art. Each of the working sections has a neutral position 121 or 122 and operating positions 123a and 123b or 124a and 12412. The working sections 116 and 117 may be operated to their respective operating positions by any suitable means.

The working sections 116 and 117 include work ports 128a, 128b, 129a and 1291) which are adapted to be connected to first and second fluid actuated devices and which correspond to work ports 34a, 34b, 35a and 35 of the control valve 30 of FIG. 1.

The control valve 115 also includes a neutral flow passage which is comprised of two series-connected control signal valves which are symbolized by flow paths 126 and 127.-

' Referring again to FIG. 3, the sensor valve 110 has a first operating position 1 11, a second operating position 112, and a third operating or bypass position 113. The sensor valve 110 is operated to these three positions by first and second fluid actuators 131 and 132 which may have equal or unequal fluid responsive areas. The sensor valve 110 may optionally include a bias force means or spring 28.

Operation of the system of FIG. 3 which includes equal areas in the actuators 131 and 132 and which includes the spring 28 is as follows: actuation of either working section, 116 or 117 toward an operating position is effective to restrict or to block a flow path 126 or 127. The restricting or blocking of a flow path 126 or 127 is effective to increase the fluid pressure or control signal pressure in conduit 133 because the flow paths 126 and 127 control flow from the conduit 133 to the sump 50c, and so flow across restrictor means or orifice 45 is effective to build up the pressure in the conduit 133 and in the actuator 131.

The sensor valve 110 is actuated to the second operating position 112 whenever the total force of actuator 131 and spring 28 is sufficient to overcome the force developed by the pressure of pump outlet pressure in the actuator 132. In the second operating position 112, pump displacement is increased by discharging fluid from the piston 16 to the sump 500 via a flow path 134.

When the force developed by the actuator 132 overcomes the force developed by the actuator 131 and the spring 28 then the sensor valve is moved to the first operating position 111 wherein the displacement of the pump 10 is decreased by flow of fluid from the pump 10 into the piston 16 via flow path 136, or, a greater force developed by the actuator 132 will move the sensor valve 110 to the bypass position 113 wherein the flow path 136 is maintained to decrease the displacement of the pump and an additional or bypass flow path 137 is established. Thus, the bypass position 113 and its bypass flow path 137 cooperate with the displacement control mechanism 14 and the piston 16 to control the effective output of the pump 10.

The operation of the FIG. 3 configuration with the actuator 131 larger than the actuator 132 is as previously described except that a lower fluid pressure in the actuator 131 is able to overcome the force developed by the actuator 132 so that the control signal valves in the working sections 116 and 1 17, as symbolized by the flow paths 126 and 127, operate at lower fluid pressures,

A pilot relief valve 140 is connected to the actuator 131 and to the sump 50c and is effective in limiting the fluid pressure and the force of the actuator 131, so that pumping pressures above a predetermined value are effective to develop a force in the actuator 132 that overcomes the force of the actuator 131 and moves the sensor valve 110 to the first operating position 111 or even on to the bypass condition 113. Thus the pilot relief valve 140 adds the function of pressure compensation to the hydraulic system.

The sensor valve of FIG. 4 shows a preferred configuration of a sensor valve that is adapted for use in the system of FIG. 3.

The sensor valve 150 includes a body 151 having a bore 152, a plunger 153 in the bore 152, a spring adapter 154, a spring 28, and a cap 155. The body 151 of FIG. 4 includes ports 156, 157, 158 and 159 which are connected by conduits 160, 161, 162 and 163 as shown in FIG. 3.

Referring again to FIG. 4, plunger 153 is in a neutral position between positions one and two and the port 157 is blocked by plunger land 166. In a second operating position, the plunger 153 is to the left of the position shown, the land 166 is not blocking the port 157, and fluid from the piston 16 is free to flow to the sump 50c via the conduit 161, a reduced diameter portion 167, a passage 168, the port 158 and the conduit 162.

In a first operating position, the plunger 153 is to the right of the position shown and fluid can flow from the conduit and the port 156 to the port 157 and the piston 16 via a reduced diameter portion 173 thereby reducing the pump displacement.

In a third or bypass position, the plunger 153 is moved further to the right than for the first operating position, so that excess pump flow is delivered to the sump 500 via the port 156, a longitudinal passage 169, a cross drilled hole 170 and an annular groove 171 in the plunger 153, and a passage 172 in the body 151.

In a fourth or supplementary bypass position, the plunger 153 is moved yet further to the right opening a supplementary bypass path from the conduit 160 and the port 156 to the port 158 and the sump 50c via the reduced diameter portion 173 and the passage 168 The advantage of the FIG. 4 construction is that the third position achieves bypass flow with a minimum movement of the plunger 153 from the first operating position; and then additional movement to the fourth operating position is effective to establish a bypass flow path having additional and larger flow capacity.

The system of FIG. 5 is the same as the FIG. 1 configuration, except that, the feedback mechanism consisting of the push rod 57 and the spring 28, the sensor valve 20, and the control piston 16 of FIG. 1 are all combined into a coaxial piston sensor valve 180, and except that, the control valve 30 of FIG. 1' is replaced by the control valve 115 of FIG. 3.

The coaxial piston sensor valve 180 includes a housing or body 181 which has a piston 182, a spring cavity 183, a partition 184 and a cap 185.

A piston 188 is slidably fitted in the bore 182 and includes a plunger bore 189. A valve plunger 190 is slidably fitted in bore 189 of piston 188 and cooperates with piston 188 to form first and second relatively movable elements of a sensor valve.

One end of the plunger 190 extends through a hole 191 in the partition 184 into the cavity 183 and thereby cooperating with the cavity 183 to form a fluid actuator means having a fluid responsive area equal to the area of the plunger 190 at the place where it extends through the hole 191.

A spring 28 placed in compression between the partition 184 and an integral shoulder 192 on the plunger 190 provides a bias force urging plunger 190 to the right.

In operation, the control signal pressure from the port 46 and a conduit 71 is applied to the spring cavity 183 and to the projected area of the plunger 190 forcing the plunger 190 to the left against the force of the spring 28.

Movement of the plunger 190 to the left moves a plunger land 193 to the left exposing a port 194 to a reduced diameter portion 195 of the plunger 190, to a cross hole 196 and an annular groove 197 in the piston 188, and to a port 198 which is connected to pump pressure by a conduit 199.

Connection of pump pressure to the port 194 is effective to pressurize chamber 202 which exists between the piston 188 and the partition 184 because of the flow path provided by a longitudinal hole 203.

Pump pressure supplied to the chamber 202 is efiective to move the port 194 to the left thereby cooperating with the land 193 to stop additional fluid flow to the chamber 202. Thus it can be seen that the plunger 190, the spring 28, the piston 188 and the swash plate 15 all cooperate to form a mechanism in which the displacement of the pump 10 is controlled to be inversely proportional to the magnitude of the control signal pressure supplied to the spring cavity 183.

In like manner, a decrease in fluid pressure in the spring cavity 183 allows the spring 28 to move the plunger 190 to the right opening chamber 202 to a sump, not shown, via the longitudinal hole 203, the port 194, the exposed left end of the land 193 and the bore 189.

The systems that have been described provide a superior method of controlling the output of any pump that includes a pressure actuated means of controlling either the actual displacement of the pump or the effective output of the pump. Thus it should be understood that the term variable displacement is used to include pumps having any control that regulates the quantity of fluid that is discharged through the pressure port.

Various features of the invention have been particularly shown and described; however, it should be obvious to one skilled in the art that modifications may be made therein without departing from the scope of the invention.

What is claimed is:

l. A hydraulic system including a variable displacement pump having a fluid actuated displacement control mechanism adapted to control the displacement of said pump, a sump, a control valve having a neutral position and an operating position and being adapted to control a fluid actuated device, and a fluid actuated device all operatively connected, the improvement which comprises:

a sensor valve connected to said pump, to said sump, and to said displacement control mechanism and being adapted to establish, to block, and to control fluid communication paths from said pump to said displacement control mechanism and from said displacement control mechanism to said sump as said sensor valve is actuated to first and second operating positions;

sensor valve actuating means adapted to provide an operating force to actuate said sensor valve from one of said operating positions to the other of said operating positions in response to a control signal pressure applied to said sensor valve actuating means;

control signal valving means and restrictor means connected in series between said pump and said sump and being adapted to receive and to control fluid pressure from said pump for use as said control signal pressure, said control signal valving means being operatively connected to and controlled by said control valve as said control valve is moved to said positions to control said fluid actuated device;

and control signal conduit means connected between said control signal valving means and said restrictor means to receive said control signal pressure and operatively connected to said sensor valve actuating means to apply said control signal pressure thereto;

whereby said control signal valving means and said restrictor means cooperate to provide and to control said control signal pressure, to actuate said sensor valve to said operating positions and to control the displacement of said pump in response to the movement of said control valve to said positions.

2. The hydraulic system as claimed in claim 1 in which said control valve includes first and second working sections adapted to be actuated to control first and second fluid actuated devices;

said control signal valving means includes a first control signal valve operatively connected to said first working section for actuation thereby and a second control signal valve operatively connected to said second control valve for actuation thereby;

said restrictor means and said control signal valves being operatively connected together and interposed between said pump and said sump;

whereby the actuation of either of said working sections is effective to control said control signal pressure and to increase the displacement of said pump.

3. The hydraulic system as claimed in claim 2 in which said control signal valves are connected in series with each other and with said restrictor means;

and closing of either one of said control signal valves is effective to control said control signal pressure and to increase the displacement of said pump. 4. The hydraulic system as claimed in claim 2 in which each of said control signal valves includes two ports;

each of said control signal valves has one of said ports in fluid communication with said pump and has the other of said ports in fluid communication with said sump;

and opening either one of said control signal valves is effective to control said control signal and to increase the displacement of said pump.

5. The hydraulic system as claimed in claim 1 in which said restrictor means is located between said pump and said control signal valving means.

6. The hydraulic system as claimed in claim 1 in which said restictor means is located between said control signal valving means and said sump.

7. The hydraulic system as claimed in claim 1 which includes a pilot relief valve connected to said pump and to said sensor valve actuating means and adapted to move said sensor valve to a displacement decreasing position by increasing thP fluid pressure applied to said sensor valve actuating means.

8. The hydraulic system as claimed in claim 1 in which said first operating position of said sensor valve is effective to control said paths to increase the displacement of said pump;

said sensor valve is effective in said second operating position to control said communication paths to decrease said displacement of said pump;

and said sensor valve includes a third operating position in which fluid communication paths are controlled to decrease said displacement and said sensor valve establishes a bypass communication path between said pump and said sump;

whereby said bypass communication path cooperates with said displacement control mechanism to control the effective output of said pump.

9. The system as claimed in claim 1 in which said sensor valve actuating means includes bias force meanS and fluid actuator means.

10. The system as claimed in claim 9 in which said sensor valve includes a sensor valve body having a bore therein and a valve plunger slidably fitted in said bore;

said fluid actuator means includes the projected end area of said valve plunger;

and a spring comprises said bias force means.

11. A hydraulic system including a variable displacement pump having a fluid actuated displacement control mechanism adapted to control the displacement of said pump, a sump, a control valve having a neutral position and an operating position and being adapted to control a fluid actuated device, and a fluid actuated device all operatively connected, the improvement which comprises:

a sensor valve connected to said pump, to said sump,

and to said displacement control mechanism and being adapted to establish, to block, and to control fluid communication paths from said pump to said displacement control mechanism and from said displacement control mechanism to said sump as said sensor valve is actuated to first and second operating positions; sensor valve actuating means including first and second fluid actuators adapted to provide operating forces to actuate said sensor valve to said first and second operating positions in response to fluid pressures applied to said fluid actuators; control signal valving means and restrictor means connected in series between said pump and said sump and being adapted to receive and to control fluid pressures from said pump to provide control signal pressures, said control signal valving means being operatively connected to and controlled by said control valve as said control valve is moved to said positions to control said fluid actuated device;

first control signal conduit means connected between said control signal valving means and said restrictor means to receive said control signal pressures and operatively connected to one of said fluid actuators to apply said control signal pressures thereto;

and second control signal conduit means connected between said pump and the other of said fluid actuators to apply fluid pressures from said pump for use as control signal pressures for said other fluid actuator;

whereby said control signal valving means and said restrictor means cooperate to provide control signal pressures applied to one of said fluid actuators, to actuate said sensor valve to said operating positions and to control the displacement of said pump in response to the movement of said control valve to said positions.

12. The hydraulic system as claimed in claim 11 which includes a pilot relief valve connected to said one fluid actuator and to said sump and effective to limit the control signal pressures applied to said one fluid actuator;

whereby pump pressures applied to said other actuator are effective to reduce the displacement of said pump by forcing said sensor valve toward a displacement decreasing position thereby forcing fluid from said one actuator to said sump whenever said pump pressures exceed a predetermined value.

13. The hydraulic system as claimed in claim 11 in which said sensor valve includes a sensor valve body having a bore therein and a valve plunger slidably fitted in said bore;

said first and second fluid actuatros include the use of the projected end areas of said valve plunger for use as fluid responsive areas;

and said valve plunger is movable to a third or bypass position wherein fluid connections are made to decrease the displacement of said pump and to bypass excess pump flow from said pump to said sump.

14. The hydraulic system as claimed in claim 11 which includes fluid actuators having unequal fluid responsive areas.

15. The hydraulic system as claimed in claim 11 in which said sensor valve actuating means includes a bias spring.

16. A hydraulic system including a variable displacement pump having a fluid actuated displacement control mechanism operably connected to said pump and movable to control the displacement thereof, a control valve having a valving element movable from a neutral position to an operating position and to intermediate positions therebet ween, a fluid actuated device operatively connected to said control valve for actuation thereby, and a fluid sump all operatively connected, the improvement which comprises:

a sensor valve having a body, a valve plunger, and a sensor valve actuating means and being connected to said pump, to said sump, and to said displacement control mechanism;

said valve plunger being operable to first, neutral,

and second positions and being adapted to cooperate with said body to establish, to block and to control fluid communication paths between said pump and said displacement control mechanism and between said displacement control mechanism and said sump to increase the displacement of said pump, to decrease the displacement of said pump, and to maintain the displacement of said pump at any given value as a function of the relative position of said valve plunger to said valve body;

said sensor valve actuating means consisting of bias force means and fluid actuator means and being operatively connected to said valve plunger and being adapted to move said valve plunger relative to said body in response to a control signal pressure applied to said fluid actuator and in proportion to the magnitude of said control signal pressure, whereby there exists a first proportional relationship between the magnitude of said control signal pressure and the relative position of said valve plunger to said body;

control signal valving means and restrictor means being connected in series between said pump and said sump to control the flow of pressure fluid between said pump and said sump, being adapted to provide a control signal pressure in the juncture between said control signal valving means and said restrictor means, and being adapted to control the magnitude of said control signal;

control signal conduit means being connected to said juncture between said control signal means and said restrictor means to receive said control signal pressure and being connected to said fluid actuator means to apply said control signal pressure thereto;

said control valving means being operatively connected to said valving element to receive movement therefrom and being adapted to control the magnitude of said control signal pressure proportional to the position of said valving element from said neutral position, whereby a second porportional relationship exists between the position of said valving element, the magnitude of said control signal pressure and the relative position of said valve plunger to said body;

said feedback means operatively interconnecting said sensor valve and said displacement control mechanism and being adapted to modify said second proportional relationship in proportion to the movement of said displacement control mechanism and the displacement of said pump;

whereby there exists a proportional relationship between the position of said valving and the displacement of said pump.

17. The hydraulic system as claimed in claim 16 in which said bias force means includes a spring;

and said feedback means includes said spring as a part of said means interconnecting said displacement control mechanism and said sensor valve.

18. The hydraulic system as claimed in claim 17 in which said pump is of axial piston type and said displacement control mechanism includes a variable inclination swash plate;

said fluid actuator means includes the projected area of one end of said valve plunger; and said feedback means includes said spring interposed between said valve plunger and said swash plate, one end of said spring being adapted to receive motion from said swash plate as the displacement of said pump is changed and the other end of said spring being adapted to apply force to the other end of said valve plunger. 19. The hydraulic system as claimed in claim 16 in which said valve plunger and said body comprises first and second relatively movable valving parts;

one of valving parts being operable to first and second positions by said bias force and said fluid actuator means;

and the other of said valving parts being operatively connected to said displacement control mechanism to receive feedback movement therefrom.

20. The hydraulic system as claimed in claim 19 in which said displacement control mechanism includes a control piston, said one valving part is coaxial with said control piston, and said other valving part is connected to said control piston to receive feedback movement therefrom.

UNITED STATES PATENT OFFICE CERTIFICATE OF- CORRECTION Patent No. 3,7 77 Dated n ry 9, 1971;

Raymond E. Johnson et a1.

Inventor(s) It is certified that error appears in the above-identifi and that said Letters Patent are hereby corrected as shown below:

ed patent Column 11, line 5, Claim 7, "12h?" should read the Column 13, line 31, "pressure" should read pressures Signed and sealed this 25th day of June 197.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents USCOMM-DC 60376-P69 us. GOVERNMFNT PRINTING OFFICE: 1969 0-365-334.

FORM PO-105O (IO-69) 

1. A hydraulic system including a variable displacement pump having a fluid actuated displacement control mechanism adapted to control the displacement of said pump, a sump, a control valve having a neutral position and an operating position and being adapted to control a fluid actuated device, and a fluid actuated device all operatively connected, the improvement which comprises: a sensor valve connected to said pump, to said sump, and to said displacement control mechanism and being adapted to establish, to block, and to control fluid communication paths from said pump to said displacement control mechanism and from said displacement control mechanism to said sump as said sensor valve is actuated to first and second operating positions; sensor valve actuating means adapted to provide an operating force to actuate said sensor valve from one of said operating positions to the other of said operating positions in response to a control signal pressure applied to said sensor valve actuating means; control signal valving means and restrictor means connected in series between said pump and said sump and being adapted to receive and to control fluid pressure from said pump for use as said control signal pressure, said control signal valving means being operatively connected to and controlled by said control valve as said control valve is moved to said positions to control said fluid actuated device; and control signal conduit means connected between said control signal valving means and said restrictor means to receive said control signal pressure and operatively connected to said sensor valve actuating means to apply said control signal pressure thereto; whereby said control signal valving means and said restrictor means cooperate to provide and to control said control signal pressure, to actuate said sensor valve to said operating positions and to control the displacement of said pump in response to the movement of said control valve to said positions.
 2. The hydraulic system as claimed in claim 1 in which said control valve includes first and second working sections adapted to be actuated to control first and second fluid actuated devices; said control signal valving means includes a first control signal valve operatively connected to said first working section for actuation thereby and a second control signal valve operatively connected to said second control valve for actuation thereby; said restrictor means and said control signal valves being operatively connected together and interposed between said pump and said sump; whereby the actuation of either of said working sections is effective to control said control signal pressure and to increase the displacement of said pump.
 3. The hydraulic system as claimed in claim 2 in which said control signal valves are connected in series with each other and with said restrictor means; and closing of either one of said control signal valves is effective to control said control signal pressure and to increase the displacement of said pump.
 4. The hydraulic system as claimed in claim 2 in which each of said control signal valves includes two ports; each of said control signal valves has one of said ports in fluid communication with said pump and has the other of said ports in fluid communication with said sump; and openiNg either one of said control signal valves is effective to control said control signal and to increase the displacement of said pump.
 5. The hydraulic system as claimed in claim 1 in which said restrictor means is located between said pump and said control signal valving means.
 6. The hydraulic system as claimed in claim 1 in which said restictor means is located between said control signal valving means and said sump.
 7. The hydraulic system as claimed in claim 1 which includes a pilot relief valve connected to said pump and to said sensor valve actuating means and adapted to move said sensor valve to a displacement decreasing position by increasing thP fluid pressure applied to said sensor valve actuating means.
 8. The hydraulic system as claimed in claim 1 in which said first operating position of said sensor valve is effective to control said paths to increase the displacement of said pump; said sensor valve is effective in said second operating position to control said communication paths to decrease said displacement of said pump; and said sensor valve includes a third operating position in which fluid communication paths are controlled to decrease said displacement and said sensor valve establishes a bypass communication path between said pump and said sump; whereby said bypass communication path cooperates with said displacement control mechanism to control the effective output of said pump.
 9. The system as claimed in claim 1 in which said sensor valve actuating means includes bias force meanS and fluid actuator means.
 10. The system as claimed in claim 9 in which said sensor valve includes a sensor valve body having a bore therein and a valve plunger slidably fitted in said bore; said fluid actuator means includes the projected end area of said valve plunger; and a spring comprises said bias force means.
 11. A hydraulic system including a variable displacement pump having a fluid actuated displacement control mechanism adapted to control the displacement of said pump, a sump, a control valve having a neutral position and an operating position and being adapted to control a fluid actuated device, and a fluid actuated device all operatively connected, the improvement which comprises: a sensor valve connected to said pump, to said sump, and to said displacement control mechanism and being adapted to establish, to block, and to control fluid communication paths from said pump to said displacement control mechanism and from said displacement control mechanism to said sump as said sensor valve is actuated to first and second operating positions; sensor valve actuating means including first and second fluid actuators adapted to provide operating forces to actuate said sensor valve to said first and second operating positions in response to fluid pressures applied to said fluid actuators; control signal valving means and restrictor means connected in series between said pump and said sump and being adapted to receive and to control fluid pressures from said pump to provide control signal pressures, said control signal valving means being operatively connected to and controlled by said control valve as said control valve is moved to said positions to control said fluid actuated device; first control signal conduit means connected between said control signal valving means and said restrictor means to receive said control signal pressures and operatively connected to one of said fluid actuators to apply said control signal pressures thereto; and second control signal conduit means connected between said pump and the other of said fluid actuators to apply fluid pressures from said pump for use as control signal pressures for said other fluid actuator; whereby said control signal valving means and said restrictor means cooperate to provide control signal pressures applied to one of said fluid actuators, to actuate said sensor valve to said operating positions and to control the displacement of said pump iN response to the movement of said control valve to said positions.
 12. The hydraulic system as claimed in claim 11 which includes a pilot relief valve connected to said one fluid actuator and to said sump and effective to limit the control signal pressures applied to said one fluid actuator; whereby pump pressures applied to said other actuator are effective to reduce the displacement of said pump by forcing said sensor valve toward a displacement decreasing position thereby forcing fluid from said one actuator to said sump whenever said pump pressures exceed a predetermined value.
 13. The hydraulic system as claimed in claim 11 in which said sensor valve includes a sensor valve body having a bore therein and a valve plunger slidably fitted in said bore; said first and second fluid actuatros include the use of the projected end areas of said valve plunger for use as fluid responsive areas; and said valve plunger is movable to a third or bypass position wherein fluid connections are made to decrease the displacement of said pump and to bypass excess pump flow from said pump to said sump.
 14. The hydraulic system as claimed in claim 11 which includes fluid actuators having unequal fluid responsive areas.
 15. The hydraulic system as claimed in claim 11 in which said sensor valve actuating means includes a bias spring.
 16. A hydraulic system including a variable displacement pump having a fluid actuated displacement control mechanism operably connected to said pump and movable to control the displacement thereof, a control valve having a valving element movable from a neutral position to an operating position and to intermediate positions therebetween, a fluid actuated device operatively connected to said control valve for actuation thereby, and a fluid sump all operatively connected, the improvement which comprises: a sensor valve having a body, a valve plunger, and a sensor valve actuating means and being connected to said pump, to said sump, and to said displacement control mechanism; said valve plunger being operable to first, neutral, and second positions and being adapted to cooperate with said body to establish, to block and to control fluid communication paths between said pump and said displacement control mechanism and between said displacement control mechanism and said sump to increase the displacement of said pump, to decrease the displacement of said pump, and to maintain the displacement of said pump at any given value as a function of the relative position of said valve plunger to said valve body; said sensor valve actuating means consisting of bias force means and fluid actuator means and being operatively connected to said valve plunger and being adapted to move said valve plunger relative to said body in response to a control signal pressure applied to said fluid actuator and in proportion to the magnitude of said control signal pressure, whereby there exists a first proportional relationship between the magnitude of said control signal pressure and the relative position of said valve plunger to said body; control signal valving means and restrictor means being connected in series between said pump and said sump to control the flow of pressure fluid between said pump and said sump, being adapted to provide a control signal pressure in the juncture between said control signal valving means and said restrictor means, and being adapted to control the magnitude of said control signal; control signal conduit means being connected to said juncture between said control signal means and said restrictor means to receive said control signal pressure and being connected to said fluid actuator means to apply said control signal pressure thereto; said control valving means being operatively connected to said valving element to receive movement therefrom and being adapted to control the magnitude of said control signal pressure proportional to the position of said valving element from said neutral position, wherebY a second porportional relationship exists between the position of said valving element, the magnitude of said control signal pressure and the relative position of said valve plunger to said body; said feedback means operatively interconnecting said sensor valve and said displacement control mechanism and being adapted to modify said second proportional relationship in proportion to the movement of said displacement control mechanism and the displacement of said pump; whereby there exists a proportional relationship between the position of said valving and the displacement of said pump.
 17. The hydraulic system as claimed in claim 16 in which said bias force means includes a spring; and said feedback means includes said spring as a part of said means interconnecting said displacement control mechanism and said sensor valve.
 18. The hydraulic system as claimed in claim 17 in which said pump is of axial piston type and said displacement control mechanism includes a variable inclination swash plate; said fluid actuator means includes the projected area of one end of said valve plunger; and said feedback means includes said spring interposed between said valve plunger and said swash plate, one end of said spring being adapted to receive motion from said swash plate as the displacement of said pump is changed and the other end of said spring being adapted to apply force to the other end of said valve plunger.
 19. The hydraulic system as claimed in claim 16 in which said valve plunger and said body comprises first and second relatively movable valving parts; one of valving parts being operable to first and second positions by said bias force and said fluid actuator means; and the other of said valving parts being operatively connected to said displacement control mechanism to receive feedback movement therefrom.
 20. The hydraulic system as claimed in claim 19 in which said displacement control mechanism includes a control piston, said one valving part is coaxial with said control piston, and said other valving part is connected to said control piston to receive feedback movement therefrom. 